In the field of spark ignition type internal combustion engines installed in motor vehicles, various types of in-cylinder or direct injection type gasoline engines have been proposed in recent years, wherein a fuel is directly injected into a combustion chamber, instead of an intake pipe as in conventional engines, in an attempt to reduce harmful components of exhaust gases, and improve fuel economy. One example of such in-cylinder injection type gasoline engines is disclosed in U.S. Pat. No. 5,305,720 (Japanese Laid-open Patent Publication (Kokai) No. 5-240044).
In the in-cylinder injection gasoline engine disclosed in the above-identified publication, each intake port is formed as an upright port that extends substantially straight in a vertical direction, so that the air is sucked into a combustion chamber with a high intake or suction efficiency, so as to produce a swirl (reverse tumble flow) in the vertical direction within the combustion chamber. A cavity is formed in the top face of the piston. In operation, the fuel is injected from a fuel injector toward the cavity, for example, during a compression stroke, so that an air-fuel mixture whose air-fuel ratio is close to the stoichiometric ratio can be formed around a spark plug at an ignition timing, due to the swirl flowing across the bottom face of the cavity, even where the amount of the injected fuel is small.
Accordingly, the in-cylinder injection gasoline engine of the above type is able to successfully fire or ignite an air-fuel mixture even if it has a large air-fuel ratio as a whole, namely, the combustion chamber as a whole contains a fuel-lean air-fuel mixture, thus showing a high combustion efficiency. Further, the amount of discharge of harmful components of exhaust gases, such as carbon monoxide (CO) and hydrocarbon (HC), can be reduced, and the fuel economy can be improved mainly during idling of the engine or running of the vehicle with a low load.
The in-cylinder injection gasoline engine disclosed in the above-identified publication is provided by constructing a DOHC (double over head camshaft) type gasoline engine so that the fuel can be directly injected into the combustion chamber or cylinder.
However, the DOHC type gasoline engine is provided with two camshafts, and therefore suffers from a problem of relatively high manufacturing cost. The use of the two camshafts also results in an increase in the dimension of a cylinder head as measured in the width direction, which eventually results in an increase in the size of an engine body. If the size of the engine body is thus increased, the size of the engine as a whole cannot be reduced even if the in-cylinder injection gasoline engine has a relatively small displacement, thus making it difficult to install the engine on the vehicle.
In view of the above problem, it may be considered to construct an in-cylinder injection gasoline engine based on a SOHC (single over head camshaft) type gasoline engine that may have a reduced size and is available at a relatively low manufacturing cost, by providing the SOHC type engine with a fuel injection valve (injector) that is able to inject the fuel into the combustion chamber formed in the cylinder.
In this case, intake and exhaust ports, spark plug and other components of the SOHC type in-cylinder injection gasoline engine need to be located at appropriate positions relative to the single camshaft, so that the in-cylinder injection gasoline engine exhibits a high combustion efficiency that is equivalent to that of the DOHC type in-cylinder injection gasoline engine as described above.